Rubber products resistant to radiation damage



United States Patent Delaware No Drawing. Filed Aug. 21, 1958, Ser. No.756,294 5 Claims. (Cl. 260--45.7)

This invention relates to rubber products resistant to radiation damage.f,

The word rubber as used herein includes both natural and syntheticrubbery materials.

Rubber vulcanizates, when subjected to ionizing radiation, undergodeterioration in stress-strain properties, this being due to chainscission and cross linking. For instance, when some vulcanizates aresubjected to radiation, such as alpha rays, beta rays, gamma rays, orneutrons, there is a considerable increase in the modulus of the productand the number of network claims, related to cross links, is increased.Other vulcanizates, when subjected to the same radiation, are degradedto softer and even liquid products. Such changes are undesirable ineither case because the physical properties of the rubber are harmed bythis radiation.

Some research has been done to determine what additives can beincorporated in the rubber to produce products which are resistant toradiation or at least more resistant than the material Without the useof such additives. These additives are referred to as radiation damageinhibitors or anti-rads. I have discovered a group of compounds whichare very eifective in reducing this deterioration or radiation damage.Broadly, the invention comprises a method comprising incorporating inrubber during the compounding thereof a compound having the formulawhere x is an integer selected from the group consisting of 1 and 2, Ris aryl and R is selected from the group consisting of aryl and hydrogenin an amount of 5 to parts per 100 parts of said rubber, vulcanizing thecomposition, and exposing the vulcanized composition to ionizingradiation of 1X10 to 5X10 roentgens, said composition having less changein modulus than the same composition without the addition of said RScompound.

The following, therefore, are objects of this invention.

An object of my invention is to provide rubber vulcanizates which areresistant to radiation damage. A further object of my invention is toprovide compositions containing certain sulfur derivatives which makethe product exhibit less change in modulus. than the same productwithout the additive. A further object of this invention is to provide amethod of reducing damage to rubber when subjected to ionizingradiation.

Other objects and advantages of my invention will be apparent to oneskilled in the art upon reading this disclosure.

The radiation inhibitors of this invention have the formula R$ -R andinclude thiols or mercaptans and monoand disulfides. One aromatic groupis required and both R and R can be aromatic, such groups being phenyland naphthyl groups. The aryl radicals 3,175,992 Patented Mar. 30, 1965can contain substituents including NO halogen; --OH; SH; SO H; OCN; NCO;SCN; NCS; alkyl; alkoxy;

where X is hydrogen, alkyl, or aryl; N=N-Y, where Y is alkyl or aryl;and mixtures thereof. Where alkyl or alkoXy groups are present eachgroup should not contain more than 4 carbon atoms and the carbon atomsin the total of such groups should not exceed 12. Specific examples ofthese compounds include thiophenol,

thio-l -n aphthol,

thio-Z-naphthol,

Q-methylthiophenol, 4-methylthiophenol, 2,3-diethyltbiophenol,2-rnethyl-4-ethylthiophenol, 2,4,6-tributylthiophenol,4-methoxythiophenol, 2,4-diethoxythiophenol,Z-methyl-6-propoxythiophenol, 1-thiopheno1-4-sulfonic acid,4-mercaptobenzonitrile, Z-mercaptophenylcyanate,3-mercaptophenylisothiocyanate, 2,6-dinitrothiophenol,4-chlorothiophenol,

4-mercaptophenol, 2,4,6-dichloro-3,5-di-n-propylthiophenol,3,5-dibromo-2,4,6-trimethoxythiophenol, 4-rnethylthio-l-naphthol,2,S-diethylthio-Z-naphthol,

4,5 -dinitrothio-1-naphthol, S-ethoxythio-Z-naphthol,4,5-dimercapto-2-naphthol, thio-l-naphthol-4-sulfonic acid,S-cyanothio-l-naphthol, 5,7-dibromothio-Z-naphthol,l,4-diethyl-7-tert-butylthio-2-naphthol, 2-mercaptonaphthyl-4-cyanate,l-mercaptonaphthyl-S-isocyanate, 2-mercaptonaphthyl-7-thiocyanate,2,4-di1nercapto-3-naphthionitrile,2,7-diiodo-4,5-dimethyltl1io-l-naphthol,2,7-di-tert-butyll-butoxythio-l-naphthol,

r 2,4,6,S-tetraethylthio-l-naphthol,

diphenyl sulfide,

1-naphthyl phenyl sulfide, 2-naphthyl phenyl sulfide, diphenyldisulfide, l-naphthyl phenyl disulfide, Z-naphthyl phenyl disuifide,di-l-naphthyl disulfide, di 2-napht hyl disulfide,bis(2,4-dinitrophenyl) sulfide,

bis(2,4-dinitrophenyl) disulfide, bis(2-nitrophenyl) disulfide,bis(4-nit1rophenyl) disulfide, bis(4-tert-butylphenyl) sulfide,bis(4'-tert-butylphenyl) disulfide, bis(2,4-dimethylphenyl) disulfide,his(2-methyl-4-isopropylphenyl) disulfide, bis(2-methyl-1-naphthyl)disulfide, bis(4-ethyl-2-naphtihyl) disulfide,bis(2,7-dimethyl-1-naphthyl) disulfide,bis(1-mercapt0-4,S-dinitro-Z-naphthyl) sulfide, bis(4-nitrophenyl)sulfide, bis(2,4-dichl'orophenyl) disulfide,bis(4-hydroxy-2,6-dimethylphenyl) disulfide, bis(3-sulfophenyl) sulfide,bis(4-cyanopheny1) sulfide, 4-rnethoxy- 2-naphthy1 phenyl disulfide, 4-(phenylmercapto phenylisocyanate, 1- (phenyhnercapto)-3-naphthylcyanate, bis(2,6-dichloro-4-nitro-3,S-dimethylphenyl)disulfide, bis(3,6-disulfo-2-naphthyl) disulfide, bis(4,5-dicyano-2,7-diethyl-l-naphthyl) sulfide,3,6-dicyan-2,4,5,7-tetramethyl-l-naphthyl 4-hydroxyphenyl sulfide,3,6-diethoxy-2-naphthyl 3,5-dibromophenyl disulfide,4-phenylmercaptoazobenzene, bis(4-aminophenyl) disulfide,bis(2,4-dimethylaminophenyl) disulfide, and bis(4-phenylazophenyl)disufide.

The amount of inhibitor employed should be at least 5 parts by weightper 100 parts by weight of rubber used. Over parts by weight is seldomnecessary and a preferred range is 5 to 7 parts by weight.

The invention is applicable to all types of rubber, both natural andsynthetic. The synthetic polymers include the groups prepared bypolymerizing a conjugated diene of 4 to 10 carbon atoms, either alone,or in combination with an unsaturated comonomer such as styrene,acrylonitrile, methacrylonitrile, methyl vinyl ether, methylmethacrylate, and the like. Generally, the conjugated diene, such asbutadiene, isoprene, heXadiene, etc., comprises a major amount of themonomer system. The invention is also applicable to polychloroprene andrubbers of the polyurethane and isocyanate types. For a more completediscussion of the various synthetic rubbers, attention is directed toWhitby, Synthetic Rubber, published by John Wiley and Sons, Inc., NewYork, 1954.

The following examples are forth specific compositions made according tothe present invention but obviously, considerable variation is possiblefrom the specific amounts set forth in the examples.

Examples A 75/25 butadiene/styrene rubber was prepared by emulsionpolymerization at 41 F. to give a polymer having a raw Mooney value(ML-4) of 52 and a bound styrene content of percent. A recipe for theproduction of such a polymer is:

Tert-dodecyl mercaptan, as required for a 52 ML-4 rubber.

1 Sodium salt of a naphthalene sulfonic acid condensed withformaldehyde.

This illbber was compounded using various inhibitors,

the amount being 5 parts by weight in each case and a control was madewith no inhibitor. The recipe was 1 Philblack O, a high abrasion furnaceblack.

2A physical mixture containing percent of a complex (liarylamine-ketonereaction product and 35 percent of N,N- diphenyl-p-phenylenediamine.

N-cyclohexy1-2-benzothiazylsulfenamide.

The stocks were roll milled, sheeted oti the mill, and cured 30 minutesat 307 F. Tensile specimens Vs wide and 2 long (length of test portion)were cut from the sheets which were 25-30 mils in thickness. Swellspecimens /2" X -l" were also cut from the sheets. The specimens werepacked into aluminum cans which were closed, purged with helium, andirradiated in a field of gamma rays from spent fuel elements from theMaterials Testing Reactor at Arco, Idaho, at a canal temperature ofapproximately F. A pressure of 25 pounds helium was maintained in thecans during irradiation. Runs were made with total dosages of l 10roentgens, 3 10 roentgens, 7 10 roentgens, and 1x10 roentgens. One setof samples was not irradiated but was reserved for control purposes. Theirradiated materials were removed from the gamma ray field and physicalproperties were determined.

In the following tables the original percent modulus is set forth aswell as the original density of network chains. In the subsequentcolumns the numerical change in these properties is set forth. Fromthese tables it is apparent that each of the inhibitors brought about areduction in change in 100 percent modulus and in the density of networkchains.

100% Modulus (p.s.i.)

Increase in psi. after Nominal Ori- Radiation Dose (10 Roentgeus) ginalNone 450 300 590 1, 410 1, 910 Thio 2-naphthol 230 180 410 660 1,020Phenyl monosulfide 370 230 450 900 1, 410 Bis(2,4-dinittophenyl)disulfidc 610 230 550 l, 020 l, 480 Bis (Z-nitrophenyl) disulfide. 340450 890 1, 320 Bis (4-nitropl1enyl)disulfide 370 200 480 870 1, 310

Density of network chainsXlO (moles/cc.) 1

Increase alter Nominal Radia- Orition Dose (10" Roentgeus) ginal None2.01 0. 71 2. l9 3. 14 4. 61 Thio-2-naplithol l. 09 0. 67 l. 38 2. 07 3.l9 Phenyl monosulfide 1. 74 O. 45 1. 23 2. 57 4. 30 Bis(,2,l-dinitrophenyl) disullide- 2. 90 0.54 1.25 2. 48 3. 72

Bis(Ll-nitrophenyl)disulfide. l. 54 O. 52 l. 50 2. 54 3. 64Bis(t-uitrophenyl)disulfid 2. 26 0. 64 1, 82 4. 24

1 The density of network chains is related to the number of crossllnksby the function where n is the number of crosslinks, 6 is the density ofthe polymer, and M is the molecular weight.

As many possible embodiments can be made of this invention withoutdeparting from the scope thereof, it is to be understood that all matterherein set forth isto be interpreted as illustrative and not as undulylimiting the invenion.

I claim:

1. A composition produced by vuleanizing in the presence of sulfur amixture of a rubbery polymer of butadiene and styrene and, per 100 partsby weight of said polymer, 5 to 10 parts of a sulfur compound selectedfrom the group consisting of phenyl monosulfide, bis(2,4- nitirophenyl)disulfide, bis(2-nitrophenyl) disulfide, and bis(4-nitrophenyl)disulfide.

2. The composition of claim 1 wherein said sulfur compound is phenylmonosuliide.

3. The composition of claim 1 wherein said suliur compound isbis(2,4-nitrophenyl) disulfide.

4. The composition of claim 1 wherein said sulfur compound isbis(2-nitrophenyl) disulfide.

5. The composition of claim 1 wherein said sulfur 15 compound isbis(4-nitrophenyl) disulfide.

6 References Cited in the file of this patent UNITED STATES PATENTS2,422,156 Wolf et al June 10, 1947 2,556,856 Swaney et al June 12, 19512,687,444 Crouch et a1 Aug. 24, 1954 2,878,175 Golub Mar. 17, 1959 OTHERREFERENCES Rubber Chem. and Technology, Imoto, v01 26, 1953, pages91-101. Pages 91 and 97 relied upon.

Bovey: Eii'ects of Ionizing Radiation on Natural and Synthetic HighPolymers, lnterscience Publishers, New York (1958), pages 2, 5, and 32.

1. A COMPOSITION PRODUCED BY VULCANIZING IN THE PRESENCE OF SULFUR AMIXTURE OF A RUBBERY POLYMER OF BUTADIENE AND STYRENE AND, PER 100 PARTSBY WEIGHT OF SAID POLYMER, 5 TO 10 PARTS OF A SULFUR COMPOUND SELECTEDFROM THE GROUP CONSISTING OF PHENYL MONOSULFIDE, BIS(2,4NITROPHENYL)DISULFIDE, BIS(2-NITROPHENYL) DISULFIDE, AND BIS(4-NITROPHENYL)DISULFIDE.